Studies were conducted to test the hypothesis that by feeding medium chain triglycerides (MCT) early in life, it might be possible to influence body fat mass, and adipose tissue cellularity in terms of fat cell size and number. Rat pups from the same dam were pair-fed either 70 percent long chain fat diet, corn oil (LCT), or medium chain triglycerides (MCT), from weaning until sacrificed at intervals up to age 28 weeks. Rats fed the MCT had significantly less adipose tissue cellularity, both in cell number and cell size, than animals fed LCT. Also studies were made of ketone body metabolism in brain slices of rats fed high levels of MCT, LCT and low fat. Results suggest that dietary-induced hyperketonemia, like starvation-induced hyperketonemia, influences brain metabolism through substrate concentration with apparent long-term inducing effects. Also, the chlyous transport of an odd carbon fat, triundecanoin, was studied in thoracic duct cannulated rats. It was possible to enhance undecanoate transport in chyle in triglyceride form by the concurrent presence in the rat meal of a long chain, low melting point triglyceride. Undecanoate, by providing the terminal moiety, propionate, is potentially glucogenic.